Cathode with dot-shaped emission

ABSTRACT

A cathode structure, particularly a MK cathode, employs a wick mounted in a coupling member adjacent a supply of emission substance, preferably barium. The wick may be formed of a number of very thin tungsten wires which are snaked or braided together and covered with a cylindrical coating of, for example, molybdenum. The wick and the emission supply substance are mounted in a housing adjacent a heater element for indirect heating. A matrix of cathodes is provided by fixing coupling members having wicks mounted therein in a spaced apart manner in an insulating plate. In such a matrix heater are disposed and secured in place between adjacent cathodes. The heaters may be jointly operated, but advantageously with different applied voltages.

United States Patent Katz [4 1 Aug. 1, 1972 CATHODE WITH DOT-SHAPED 3,259,782 7/1966 Shroff ..3l3/346 R X EMISSION FOREIGN PATENTS OR APPLICATIONS [72] Inventor: Helmut Katz, Munich, Germany 796,424 6/1958 Great Britain ..3l3/336 [73] Assignee: Siemens Aktienhaft, Berlin and Mumch Germany Primary Examiner-John K. Corbin [22] Filed: Nov. 25, 1970 Assistant Examiner-Toby H. Kusmer [2]] pp No: 92,608 Anorney-Hill, Sherman, Merom. Gross & Simpson [57] ABSTRACT [30] Foreign Application Priority Data A cathode structure, particularly a MK cathode, em-

Dec. 17, 1969 Germany ..P 19 63 333.1 ploys a wick mounted in a coupling member adjacent a supply of emission substance, preferably barium. [52] US. Cl. ..................3l3/336, 313/343, 3l3/345, The wick may be formed of a number of very thin l 4 DC tungsten wires which are snaked or braided together [51 III. C]. 1] 1/14 and govered with a cylindrical coating of for example of R, molybdenum 'rhe wick and he emission supply ub- 3 I 3/346 DC stance are mounted in a housing adjacent a heater element for indirect heating. A matrix of cathodes is pro- [56] Reimnces Cited vided by fixing coupling members having wicks UNITED STATES PATENTS mounted therein in a spaced apart manner in an insulatlng plate. In such a matrix heater are disposed and Antoms et al. R ecured in lace between adjacent cathodes The g 2 1 3322; heaters may be jointly operated, but advantageously a Z h t d 2,499,192 2/1950 Lafferty ..3l3/346 DC app m M 3,453,478 7/1969 Shoulders et al..........3l3/336 X ll Claim, 2 Drawing Figures 5 as; \1.\ 5 t PAIENTEDwc 1 1922 Too \NVENTOR ATTYS.

CATHODE wmt DOT-SHAPED EMISSION BACKGROUND OF THE INVENTION 1 Field of the Invention This invention relates to a dispenser cathode, particularly an MK cathode of cylindrical shape, which cathode has a very small frontal emission surface which is formed by a porous tungsten member, and to the method of production for such cathode.

2. Description of the Prior Art Dispenser cathodes are of particular importance in the construction of electron-beam tubes for which a very fine electron beam is highly important, such as picture recording tubes, picture reproduction tubes and oscillograph tubes. These cathodes also find advantageous application in tubes for electron microscopes and tubes which require plurality of micro-cathodes which are arranged in the configuration of a matrix. Difficulties occur in providing a sufliciently productive and sufficiently long effective layer for cathodes having a dot-shaped emission. In addition, over heating during operation is a problem in that it is difficult to apply heat which is required during operation to the small emission surface without overly heating the direct environment, particularly in view of the most often needed control mechanisms. In the majority of cases, such cathodes are embodied as wire-shaped, directly-heated cathodes. However, a direct heating is often not practical.

SUMMARY OF THE INVENTION Therefore, the primary object of the present invention is to provide an indirectly-heated cathode with a delivery mechanism which avoids the difficulties and drawbacks stated above for prior art constructions.

This objective is realized by the present invention, through the provision of a dispenser cathode, particularly a cylindrically shaped MK cathode having a very small emission surface, which emission surface is formed by a porous tungsten member. The porous tungsten member comprises a number of very thin tungsten wires, possibly snaked or braided together with a diameter of, for instance, 6 pm, which wires are held together with a cylindrical coating (shell) as a porous tungsten member in the configuration of a wick, and which wires, together with the coating thereon, are closely and centrically inserted and fixed to a coupling member which may cover a supply of emission material directly, or indirectly through the interposition therebetween of a porous tungsten disc or a tungstenwire wadding. However, the wick itself may, of course, be impregnated" with a suitable supply of emission material.

When such a cathode is arranged in a beam produc' ing system, an additional particular beam-shaping electrode or a corresponding embodiment of an alreadypresent electrode is usually also provided. With particular advantage, this construction can be provided with the cathode as described above by affixing to the coupling member a desired beam-shaping member with as little heat contact as possible.

On the other hand, however, there are electron tubes with more or less specialized electron beam operation comprising a plurality of very small cathodes, i.e. cathodes with minimum emission surfaces, which are arranged separate from one another, possibly in a matrix, the heating of which is to be effected jointly; however, the potential control of the cathodes is to be efiected separately. Such an arrangement of a matrix of micro-cathodes is advantageously provided by the utilization of a common insulating plate, for instance made of Al,0,.into which a desired number of holes are provided, into holesthe coupling members of the individual cathodes are inserted andfused, while inserting small ceramic tubes The heating wires are inserted between the small ceramic tubes on one side of the insulating plate and secured thereto by filling of a heater putty substance, suchas up,

For the production of such cathodes, special technology and technique are required. This is effected in a way that a group of closely-packed, thin tungsten wires up to a diameter of approximately l0 pm are formed into a wick, covered with a molybdenum suspemion up to a diameter in the range of from through 200 pm (sprayed on) and sintered together. The wicks are then tightly inserted into cylindrical coupling members for instance by a press fit or by soldering.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects, features and advantages of the invention, its organization, production, construction and operation will be best understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. I is an elevationalview in cross section of an individual cathode constructed in accordance with the principles of the present invention; and

FIG. 2 is an elevational view, in cross section, of a plurality of micro-cathodes which are constructed in accordance with the principles of the present invention and which are arranged in a matrix configuration.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. I, a cylindrical individual cathode is illustrated, which cathode is designed as an MK cathode with a wire-rope member 1 which is embodied as a wick. The wick l is covered with a coating 2 and mounted with its frontal top (end) as an emission surface in a coupling member 3. A supporting cylinder 14 and the coupling member 3 form a chamber 4 which houses a supply of emission material 5, preferably barium. A porous tungsten disk 6, or in its place a tungstenwire wadding, is inserted in the chamber 4 between the supply of emission substance 5 and the end (lower end of the drawing) of the wick as a lateral tightly-closing member of the housing formed by the coupling member 3 and the cylinder 14.

The cylinder 14 is closed oh by means of an inverted pot-shaped cylindrical member which has a heater 8 mounted therein by the means of a heater putty material 10. The heater can, of course, be arranged on the outside of the container due to space requirements or for other reasons.

For the case where a beam-shaping electrode is needed, such an electrode 9 may be connected to the coupling member 3 in a manner that it is sufficiently spaced from the coating to of the wick l or from the respective range of the coupling member. The affixation of the electrode 9 and the coupling member 3 may be provided by means of thread 3, 9' of the respective members 3 and 9. Such a beam-shaping may be produced with particular advantage from carbon, due to the favorable electron tube technical properties of that material.

FIG. 2 illustrates a section of an arrangement of several individual cathodes wherein a number of wicks l are arranged in the form of a matrix. Analogous parts with regard to FIG. 1 are provided with equal reference characters in FIG. 2. An insulating plate 11 having a plurality of circular holes 12 is provided, for instance from A1 0,, to form the basis of the matrix structure. Each cathode is inserted with its coupling member 3 in a respective one of the holes 12. The cathode comprises a wire wick l in a coupling member 3 having a chamber 4 holding a supply of emission material 5. The chamber 4 is sealed at the end opposite the wick l by a member 15 after the emission material is inserted. lnsertion of the emission material may also be provided by impregnation of the wires with such emission material. The coupling member 3 includes a flange 16 which bears against the upper surface of the insulating plate ll. The insulating plate I] is captured between the flange l6 and a small insulating tube 13 which is pushed over the lower end of coupling member 3. The coupling member 3 also includes a thin edge 17 which is flared or bent over the free end of the insulating tube ill to provide a firm affixation of the coupling member 3 and the insulating plate 11.

Heating wires 8, which may be pre-insulated, are placed into the interspaces between the small insulating tubes 13; then the interspaces are filled out, in addition, with a heater-putty substance 10. After the emission supply material 5 is inserted and the cathodes are closed with the members 15, a heatable aggregate results in which the individual cathodes are positioned at very small distances and in which all cathodes may be heated in common but loaded with different voltages without the danger of leakage currents.

Although I have described my invention by reference to specific illustrative embodiments, many changes and modifications may be made therein by one skilled in the art without departing from the spirit and scope of the invention, and I intend to include within the patent warranted hereon all such changes and modifications as may reasonably and properly be included within my scope to my contribution to the art.

What I claim is:

I. An indirectly heated dispenser cathode with a very small accurate planar frontal emission surface formed by a porous tungsten member, comprising: a plurality of intertwined tungsten wires; a coating on said wires outside of the emission surface to form a stable compact wick as said porous tungsten member; and housing means providing a supply chamber for emission substances mounting said wick above said chamber.

2. A dispenser cathode according to claim 1, comprising an emission substance impregnated into the wick.

3. A dispenser cathode according to claim 1, wherein said housing means includes means defining said supply chamber for emission substances and a coupling member having a passageway extending from the exterior of said housing means to said chamber and i i'l f ifis g fii flifi hccomm to claim 1, comprising a heater mounted in said housing means.

5. A dispenser cathode according to claim 1, wherein said housing means includes means defining said supply chamber, an emission substance in the chamber, means defining a cavity for mounting a heater, a heater mounted in the cavity, and a coupling member having a passageway therethrough, said passageway extending from the chamber to the exterior of said housing means, and said wick mounted in said passageway.

6. A dispenser cathode according to claim I, wherein said wick is formed of a plurality of tungsten wires having a diameter of about 6 pm, which contact each other.

7. A dispenser cathode according to claim I, wherein said wick has a diameter in the range of from to 200 pm.

8. A dispenser cathode according to claim 1, wherein said coating on the tungsten wires outside of the emission surface comprises molybdenum.

9. A dispenser cathode according to claim 1, comprising a beam shaping electrode surrounding and spaced from said wick and secured to said housing means.

10. A dispenser cathode according to claim 1, comprising a plurality of said housing means and a plurality of coated wicks mounted in respective ones of said housing means, said pluralities of housing means and wicks arranged independently in the form of a matrix; an insulating plate having a plurality of holes therein in the form of the matrix, each of said housing means mounted in respective ones of the holes; a plurality of heaters disposed between the spaced apart housing means; and means securing said heaters to said plate, each of said cathodes adapted for separate control.

11. A dispenser cathode according to claim 10, wherein said plate includes A1 0 and said securing means includes an A1 0 putty. 

2. A dispenser cathode according to claim 1, comprising an emission substance impregnated into the wick.
 3. A dispenser cathode according to claim 1, wherein said housing means includes means defining said supply chamber for emission substances and a coupling member having a passageway extending from the exterior of said housing means to said chamber and mounting therein said wick.
 4. A dispenser cathode according to claim 1, comprising a heater mounted in said housing means.
 5. A dispenser cathode according to claim 1, wherein said housing means includes means defining said supply chamber, an emission substance in the chamber, means defining a cavity for mounting a heater, a heater mounted in the cavity, and a coupling member having a passageway therethrough, said passageway extending from the chamber to the exterior of said housing means, and said wick mounted in said passageway.
 6. A dispenser cathode according to claim 1, wherein said wick is formed of a plurality of tungsten wires having a diameter of about 6 Mu m, which contact each other.
 7. A dispenser cathode according to claim 1, wherein said wick has a diameter in the range of from 100 to 200 Mu m.
 8. A dispenser cathode according to claim 1, wherein sAid coating on the tungsten wires outside of the emission surface comprises molybdenum.
 9. A dispenser cathode according to claim 1, comprising a beam shaping electrode surrounding and spaced from said wick and secured to said housing means.
 10. A dispenser cathode according to claim 1, comprising a plurality of said housing means and a plurality of coated wicks mounted in respective ones of said housing means, said pluralities of housing means and wicks arranged independently in the form of a matrix; an insulating plate having a plurality of holes therein in the form of the matrix, each of said housing means mounted in respective ones of the holes; a plurality of heaters disposed between the spaced apart housing means; and means securing said heaters to said plate, each of said cathodes adapted for separate control.
 11. A dispenser cathode according to claim 10, wherein said plate includes Al2O3 and said securing means includes an Al2O3 putty. 